The present invention relates to an alarm system for electrical devices, and more particularly to an alarm system that detects whether or not an electrical device is plugged in by sensing the alternating current (AC) radiation in the electrical power cord of the electrical device.
Various types of alarm systems have been designed in the past for purposes such as theft prevention and safety, for example. In the safety area, various systems have been designed to warn of the presence of high voltages. For example, U.S. Pat. No. 3,786,468 to Moffitt discloses an electric field proximity safety detector that enables a worker, for example a crane operator, to detect the presence of a dangerous power line or other electrical source and to maintain a safe distance from it. However, there is no disclosure of an alarm system which can detect whether or not the electrical power cord of an electrical device is plugged in to a source of AC power.
In the area of theft prevention, various protection systems have been designed to prevent the theft of a portable device by sensing whether the electrical power cord of the portable device is plugged in to the electrical outlet. For example, in U.S. Pat. No. 4,237,450 to Canez, an appliance theft alarm system is described as being capable of detecting the removal of the electrical power cord of a portable electrical device, such as a television, from the power outlet. If a thief tried to steal the device, an alarm signal would be generated upon the power cord's being unplugged. However, the Canez alarm system has a number of disadvantages. A primary disadvantage is that it requires the electrical power cord of the device to be tapped into in order to connect the AC power source to the Canez alarm system. The need to make such a tap would likely discourage use of the Canez system and may well present a fire or electric shock safety hazard in case the tap was not made correctly.